Launch Reliability: A two stage to orbit launch vehicle with engine out capability in both stages. Combined with a launch abort system for the CM (Command Module), this would be a safer manned launch vehicle than the Ares I and could be the safest manned launched vehicle ever developed.

Commercial Viability: With a probable payload capacity of 30 tonnes plus, the this vehicle should be capable of easily delivering an Orion capsule, Boeings CST-100 capsule, or a Dream Chaser space plane easily into orbit plus at least 10 to 20 tonnes of liquid hydrogen and oxygen fuel to LEO orbiting fuel depots for manned beyond LEO missions within cis-Lunar space. Hydrogen and oxygen can also be used as backup electric power aboard a space station using fuel cells with water as a valuable by product. Oxygen, of course, could be used to supply air to a space station.

Launch Reliability: A two stage to orbit vehicle with no engine out capability in the upper hypergolic stage. This makes this an inherently less reliable two stage spacecraft than the SD-CV/ ACES 41 SM but still more reliable than an Ares I.

Launch Reliability: A two stage to orbit launch vehicle with engine out capability only in the second stage.

Environmental Impact: First stage utilizes greenhouse gas polluting RP-1 (Refined Petroleum 1) fuel with liquid oxygen. However, the production of RP-1 rocket fuel from carbon neutral resources may be a possibility in the near future.

Commercial Viability: Should be able to lift an Orion capsule (without the SM) and a Boeing CST-100 into orbit. However, launching the much heavier Dream Chaser space plane with a rear positioned LAS (Launch Abort System) may require additional solid rocket boosters which would inherently lower the space vehicle's launch reliability relative to other vehicles.

Falcon 9

Launch Reliability: A two stage to orbit vehicle with engine out capability only in the first stage. The Falcon 9 should be inherently safer than the Ares 1.

Environmental impact: Both first and second stages utilizes greenhouse gas polluting RP-1 (Refined Petroleum 1) fuel with liquid oxygen which would make the Falcon 9 the least green of any crew launch vehicle. However, the production of RP-1 rocket fuel from carbon neutral resources may be a possibility in the near future.

Commercial Viability: The Falcon 9's high inherent launch safety should be attractive to customers for manned spaceflights. Space X argues that the Falcon 9 could be the cheapest manned launch vehicle ever developed.

Ares I

Launch Reliability: A two stage to orbit vehicle with no engine out capability in the solid rocket booster first stage and no engine out capability in the single engine LOX/LH2 second stage. So the Ares I would be inherently less safe than the SD-CV, Atlas V, and Falcon 9 launch vehicles.

Environmental Impact: Upper stage uses carbon neutral liquid hydrogen/oxygen fuel that's easy to derive from carbon neutral resources (nuclear, hydroelectric, wind, solar, etc.) via the electrolysis of water. The CO2 produced from the polymers contained in the single solid rocket booster would be relatively tiny compared to the CO2 pollution that would be produced from vehicles such as the Atlas V and the Falcon 9.

Commercial Viability: It seems doubtful that private companies would be attracted to launching humans aboard a spacecraft with a liquid hydrogen/oxygen upper stage on top of a huge solid rocket booster.

Man-rated SD-HLV

Launch Reliability: Three boosters are required to reach orbit. And there is with no engine out capability in the two SRBs (solid rocket boosters). This makes the SD-HLV inherently less safe than the Ares I and a lot less reliable than both versions of the SD-CV.

Environmental Impact: Core booster uses carbon neutral liquid hydrogen/oxygen fuel that's easy to derive from carbon neutral resources (nuclear, hydroelectric, wind, solar, etc.) via the electrolysis of water. The CO2 produced from the polymers contained in the two solid rocket boosters is relatively tiny compared to the CO2 that would be produced from vehicles such as the Atlas V and the Falcon 9.

Commercial Viability: Because of the unnecessary addition of two SRBs, this would be a much more expensive manned launch vehicle than the SD-CV, Atlas V, or a Falcon 9. However, these cost might be mitigated if the cargo shroud also carried valuable cargo such as multiple satellites, hydrogen and oxygen for space depots, and water and oxygen for space stations. With a minimal payload capacity of at least 65 tonnes, the SD-HLV should be able to carry crew plus at least 40 to 50 tonnes of cargo to orbit-- which is much more cargo than the Space Shuttle.

Sidemount Shuttle

Credit NASA

Launch Reliability: Three boosters are required to reach orbit with no engine out capability in the two solid rocket boosters (SRBs). This makes the SD-HLV statistically not as safe as the Ares I and a lot less safe than an SD-CV. The placement of the crew capsule and LAS (launch abort system) on the side of the external tank also makes the Sidemount less safe than the inline SD-HLV.

Environmental Impact: Core booster uses carbon neutral liquid hydrogen/oxygen fuel that's easy to derive from carbon neutral resources (nuclear, hydroelectric, wind, solar, etc.) via the electrolysis of water. The CO2 produced from the polymers contained in the two solid rocket boosters is relatively tiny compared to the CO2 that would be produced from vehicles such as the Atlas V and the Falcon 9.

Commercial Viability: Because of the two SRBs, this would be a much more expensive manned launch vehicle than the SD-CV, Atlas V, or a Falcon 9. But like the SD-HLV, these cost might be mitigated if the cargo shroud also carried valuable cargo such as multiple satellites, hydrogen and oxygen for space depots, and water and oxygen for space stations.

Man-rated Delta IV Heavy

Launch Reliability: Three core stages and perhaps an upper stage would be required to transport humans to orbit. There would be no engine out capability in the three cores stages. This vehicle would be less inherently safe than the Ares I and only the LAS ( Launch Abort System) makes the Delta IV heavy inherently safer launch than the Space Shuttle.

Commercial viability: Should be capable of delivering an Orion capsule, Boeing CST-100, or a Dream Chaser space plane into orbit plus 10 to 20 tonnes of liquid hydrogen and oxygen fuel to LEO orbiting fuel depots.

Space Shuttle

Launch Reliability: Three boosters are required to reach orbit with no engine out capability in the two solid rocket boosters (SRBs). No LAS (Launch Abort System). However, there has only been one fatal launch accident in the nearly 30 year launch history of the Space Shuttle with no fatal launch accidents in the last 24 years.Environmental Impact: Core booster uses carbon neutral liquid hydrogen/oxygen fuel that's easy to derive from carbon neutral resources (nuclear, hydroelectric, wind, solar, etc.) via the electrolysis of water. The CO2 produced from the polymers contained in the two solid rocket boosters is relatively tiny compared to the CO2 that would be produced from vehicles such as the Atlas V and the Falcon 9.

Of the crew launch options presented above, the SD-CV with an ACES 41 upper stage would have the safest inherent crew launch architecture. The Atlas V, the Falcon 9, and Boeing's SD-CV with a stretched hypergolic SM (Service Module) would be the next most inherently reliable launch vehicles with configurations inherently more reliable than the Ares I. Because of the addition of a LAS (Launch Abort System) the SD-HLV, Sidemount Shuttle, and a man-rated Delta IV heavy would be inherently safer than the Space Shuttle but still less reliable in their architecture than the less complex Ares I.

The SD-CV and the Delta IV heavy would have the least environmental impact as far as global warming is concerned while the JP-1 fueled Atlas V (first stage) and Falcon 9 (first and second stages) would have the most deleterious greenhouse effect on the environment. While the global environmental impact of manned space launches (less than a dozen per year) is currently meager compared to other manned transportation systems, the emergence of space tourism could dramatically increase the number of manned space launches to hundreds or even thousands by mid-century as the high demand for manned spaceflights begins to dramatically reduce the cost of rocket engines and space vehicles in general. And this doesn't include the the growing demand for commercial and military satellites and space solar power satellites. Therefore, NASA needs to join the US military in helping to develop aerospace fuels that are derived from carbon neutral resources in order to mitigate the environmental impact of global warming from government and private commercial launched space vehicles.

"The knowledge that we have now is but a fraction of the knowledge we must get, whether for peaceful use or for national defense. We must depend on intensive research to acquire the further knowledge we need ... These are truths that every scientist knows. They are truths that the American people need to understand." (Harry S. Truman 1948).